1. Field of the Invention
The present invention relates to a waveguide type optical device and a method for manufacturing the same.
In the field of optical fiber communications, various optical devices, such as optical exchanges, optical multiplexers/demultiplexers, optical switches, and optical couplers, other than optical transmitters and optical receivers, are used. In optical devices of various types, there are those of the waveguide type. The waveguide type optical device is constructed by forming an optical waveguide on a waveguide substrate and, therein, a light beam is adapted to be controlled while it is confined in the optical waveguide. Devices of this type have such merits that they can be easily miniaturized because of their configuration and mass-produced by using planar techniques. Moreover, an electric or magnetic field can be easily applied thereto.
2. Description of the Related Art
Heretofore, in coupling a waveguide type optical device to an optical transmission line, it has been practiced to adjust the position of an optical fiber individually with respect to the exciting end of the optical waveguide and to securely fix the exciting end of the optical waveguide and the optical fiber with an optical binder having a specified index of refraction. Otherwise, having a groove or a pair of protrusions formed on the waveguide substrate, it has been attempted to mount the optical fiber in the groove or between the pair of protrusions to thereby eliminate the need for the positional adjustment of the optical fiber.
When the former of the above described conventional arts is used, there arises a problem that a long time is required for positional adjustment of the optical fiber and complicate work is required for coupling the optical waveguide with the optical fiber. On the other hand, when the latter of the conventional art is used, the thickness of the waveguide layer, for which a groove or a pair of protrusions are provided, tends to vary from product to product on account of difficulties involved in the fabrication technology, and this makes it difficult to achieve accurate coupling of the optical waveguide with the optical fiber. Especially, when a single-mode fiber whose core diameter is 5 to 10 .mu.m is to be coupled with an optical waveguide, since it is difficult to obtain the thickness of the waveguide layer within a tolerance of 1 .mu.m while it is required that the positioning accuracy should be within 1 .mu.m, it is practically impossible to eliminate the need for the positional adjustment in the direction of thickness of the waveguide layer. The coupling loss increases when the optical waveguide and the optical fiber are not accurately coupled. The above problems occur not only when an optical fiber is coupled with an optical waveguide but also when another optical element, such as a light emitting device and a photodetecting device, is coupled with the optical waveguide.